<i>N</i>-Alkylation of Dopamine and Its Impact on Surface Coating Properties

Surface coating with dopamine (DA) has received significant attention over the past decade due to its compatibility with other surface coating techniques and versatility, making it applicable to solid surfaces regardless of substrate and shape. Much effort has been made to elucidate the origin of its surface coating capability, and as a result, many important factors affecting the coating properties have been determined. For example, it has been reported that the length of the carbon chain between catechol and amino groups, the attachment of specific functional groups to the catechol ring and amino group, and the replacement of the amino group with another functional group can affect the surface coating properties of DA. Despite these various attempts, there are still many factors that remain unknown. In this study, we investigate the effect of <i>N</i>-alkylation on DA coating. <i>N</i>-Ethyl-DA, <i>N</i>-propyl-DA, and <i>N</i>-isopropyl-DA are newly synthesized through simple organic reactions, and the coating efficiency of DA derivatives is compared with nucleophilicity and steric bulkiness. As a result, the coating efficiency of <i>N</i>-ethyl-DA and <i>N</i>-propyl-DA is lower than for pristine DA and <i>N</i>-methyl-DA, but it is possible to coat solid surfaces with alkyl-functionalized DA. In contrast, the coating with sterically bulky <i>N</i>-isopropyl-DA is almost unsuccessful.